One of the main components in fiber optics based communications networks is the T-coupler. Most T-couplers are designed for fiber bundle implementation. In one type, the incident light from the whole input port bundle, which includes both low order and the lossy higher order modes from each of the separate fiber optic strands, is permanently split and coupled into the other T-coupler ports. In another type the strands instead of depending on cable furcation or gross division of light without regard to the order of the mode of propagation is based on using only the higher order, lossy modes of single fiber optics whether the cable is single fiber or fiber bundle. This allows for T-couplers that discriminate on modes, are applicable to single fiber operation, are small in size or weight, allow for easy alignment, and for direct optical to electrical conversion as compared to present T-couplers.
An important feature of this invention is the use of only the lossy higher order propagation modes of light, in fiber optic single strand or bundled cable, to provide an energy basis for the simplex T-coupler. An additional feature is that the degree of coupling to only the higher order modes can easily be controlled after the coupler is installed. Also the concept is applicable to either bundle, without separate fiber separation or to single fiber cable.
It is emphasized that the invention eliminates the restrictions on present fiber optic communications networks utilizing T connectors such as number of users and, once installed, on line control of the degree of coupling within the T-coupler. The control over the degree of coupling enables easy system optimization with regard to energy distribution among users when adding or substracting users. Coupling via only the higher order modes allows the maintenance of a low throughout loss while allowing for more T-couplers to be placed in series than presently achievable.
It is noted that the efficient energy utilization and applicability to single fiber cable encourages the use of single fiber employments with many T-coupled users with its consequent weight, cost and volume reductions as compared to fiber bundle installations on USAF bases and aircraft data bus applications.